1. Field of the Invention
The invention relates to a collet chuck, more particularly to a collet chuck provided with a movable member which can be driven hydraulically in two opposite directions for operating a collet.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional collet chuck is shown to include a tubular body 11, a rotating shaft 14 journalled in the tubular body 11 and provided with a frustoconical recess 162, and a collet 12 disposed operably within the frustoconical recess 162 in the rotating shaft 14 for holding a rod-shaped workpiece (A) therewithin.
As illustrated, the tubular body 11 includes a hollow main body with open front and rear ends. A tubular shaft seat 13 is confined within the tubular body 11, and defines front and rear bearing-retention recesses 131 at opposite ends thereof. Two ball bearings 18 are disposed in the bearing-retention recesses 131 in the shaft seat 13 to permit rotation of the rotating shaft 14 within the shaft seat 13. A front cover 121 is disposed fixedly on the front end of the tubular body 11 to prevent removal of the rotating shaft 14 from the tubular body 11. A rear cover 17 is disposed fixedly on the open rear end of the tubular body 11, and has a plurality of bolt holes. The fastener bolts 172 extends respectively through the bolt holes in the rear cover 17 to engage threaded holes in the rotating shaft 14, thereby preventing removal of the rotating shaft 14 from the tubular body 11. A belt pulley 173 is sleeved fixedly on the rear cover 17. The rotating shaft 14 consists of an inner sleeve 16 in which the frustoconical recess 162 is formed, and an outer sleeve 141 sleeved fixedly on the inner sleeve 16 so as to define an accommodating chamber 142 therebetween at a rear end thereof. The front cover 121 has an inner surface which is formed with a driving shoulder (121S) that abuts against a driven shoulder (12S) of the collet 12. A tubular movable member 15 is mounted axially, movably and sealingly within the accommodating chamber 142 in the outer sleeve 141 and is further fastened securely to the inner sleeve 16. A plurality of spring-retention elements 174 position a compression spring unit 175 between the rear cover 17 and the rotating shaft 14 in such a manner that the spring unit 175 biases the movable member 15 in a forward direction such that the inner sleeve 16 moves synchronously with the movable member 15. Under this condition, when the rod-shaped workpiece (A) is inserted into the collet 12, and when the front cover 121 is tightened, the workpiece (A) will be compressed radially by the collet 12 due to relative sliding movement between inclined surfaces 162xe2x80x2,123 of the inner sleeve 16 and the collet 12, as best shown in FIG. 1.
The tubular body 11 further has an oil chamber 153 that is located immediately in front of the movable member 15. Two oil passages 143, 132 are in fluid communication with the oil chamber 153. When it is desired to release the workpiece (A) from the collet 12, hydraulic oil can be fed to the oil chamber 153 via the oil passages 143,132, thereby compressing the spring unit 175 within the tubular body 11 and consequently moving the movable member 15 and the inner sleeve 16 in a forward direction away from the frustoconical recess 162, as shown by the horizontal arrows in FIG. 2, so as to release the workpiece (A) from the collet 12.
Some disadvantages that result from the use of the aforesaid conventional collet chuck are as follows:
The clamping force of the collet 12 depends entirely on the spring unit 175 and cannot be adjusted. In addition, the spring 175 suffers from spring fatigue after long term use, thereby resulting in an eventual poor clamping effect of the collet 12.
Therefore, the object of this invention is to provide a collet chuck having a movable member which can be driven hydraulically in two opposite directions for operating a collet, thereby enabling the collet to provide an effective clamping force on a workpiece.
Accordingly, a collet chuck of the present invention includes a tubular body, a rotating shaft assembly, a belt pulley, a collet, and a movable member. The tubular body has a front end and a rear end. The rotating shaft assembly is journalled within the tubular body, and has a frustoconical recess. The belt pulley is sleeved fixedly on the rotating shaft assembly. The collet is disposed operably within the frustoconical recess in the rotating shaft assembly, and is adapted to hold a rod-shaped workpiece therewithin. The movable member is mounted axially and movably within the tubular body in such a manner so as to be movable in a selected one of a tightening direction and a loosening direction. A front oil chamber is formed in the tubular body, and is located immediately in front of the movable member. A rear oil chamber is formed in the tubular body, and is located immediately behind the movable member. A first oil passage is formed in the tubular body, and is in fluid communication with the front oil chamber so that hydraulic oil can be fed to the front oil chamber therethrough, thereby moving the movable member rearward within the tubular body. A second oil passage is formed in the tubular body, and is in fluid communication with the rear oil chamber so that hydraulic oil can be fed to the rear oil chamber therethrough, thereby moving the movable member forward within the tubular body. Movement of the movable member in the tightening direction results in further movement of the collet into the frustoconical recess in the rotating shaft assembly for compressing the collet. Movement of the movable member in the loosening direction results in movement of the collet away from the frustoconical recess in the rotating shaft assembly so as to be adapted to release the workpiece from the collet.